This study uses four ongoing surveys to examine the effects of large changes in the American child support enforcement system on child support payments and child well-being. Information on state child support enforcement laws and practices is linked to these surveys, and the data are used to address four major questions: (1) What are the trends in child support laws, practices, and payments during the l98Os and l990s, and how have they changed over time nationally and in different states? (2) What are the proximate determinants of trends? To what extent can variation in payments across states and over time be explained by variation in state laws and practices? To what extent are child support laws and practices driving the trends? (3) How has child well-being changed over this period both nationally and in different states? (4) What are the proximate determinants of the trends in child well-being, and to what extent are the trends related to changes in payments? Is there a causal relationship between payments and child well-being, and if so, what are the mechanisms underlying the relationship? The analyses are based on the CPS-Child Support Supplements, 1979-1996; the SIPP panels, 1984-1996; the NLSY-Child Supplement surveys, 1986-94 waves; and the National Survey of Families and Households, 1987 and 1992 waves. All of these data sets contain information on child support payments and at least one aspect of children's well-being. Together they allow us to assess the effects of child support payments on pre-school children, children in middle childhood, adolescents, and young adults. The samples include children born to married parents as well as unmarried parents, and they are representative of white-, black-, and hispanic- Americans. The analysis is divided into two parts. Part I focuses on the relationship between child support policies and child support payments. We analyze total payments, as well as many of its components: whether paternity is established, whether there is an award, the amount of award, whether any payments are received, and the collection rate (amount paid/amount owed). The second part of the analysis focuses on the relationship between child support payments and child well-being. Here we use an instrumental variables approach to estimate the effects of payments. We estimate both reduced form models and structural models. The structural models allow us to test several hypotheses about the mechanisms underlying the relationship between payments and child well- being. We test for both an income effect and a father-involvement effect, both of which are expected to affect child well-being directly and indirectly through mother's remarriage and labor supply, residential mobility, and parental conflict.